Axial-flow compressor



Feb. 17, 1953 A. KANTRowlTz 2,628,758

v AxIAL-FLow COMPRESSOR Filed March 27, 1946 2 SHEETS-SHEET: 2

v I V EN TOR.

N QH.

Patented Feb. 17, `1953 UNITED STATES PATENT OFFICE AXIAL-FLOWCOMPRESSOR ArthurfKantrowitz, Hampton, Vai ApplicationMa-rclr 2&7, 1946,Serial. No.. 657,529

, Thisinvention relates to the-shapes of. blades for use'in anaxial-flow, compressor, andlis.I intended to produce aahigherpressureratio per stage than Yhash-ithertobeen; effected. in this type ofmachine. Heretofore, in orderv tol-achievehigh efficiency in machines ofthis type, the local gas velocities entering the rotors and stators havebeen restricted tov less.` than the velocity of sound inthe gas. Thishas; meant thatthe. compression ratio producedfby'an axial-flowcompressor stage has1 been. restrictecilv to about 1,:;3.

It is, aIrobj-ect of this` invention. to provide an improved method" forcompressing lgas so that a largevr compression; ratio;v can: be obtainedsin a singleystage and. Witlrhigh eiliciency. n

Anotherfobjectistoprovide an improved blade shape; and correlation. of;bla-ding` for effecting larger compression ratios; nzsingle stage,axial.- flow' compressors.

With this* inventionsupersonic: gas; velocity is used and the: resultingsho-ck; Waves; are controlled'so.v that high. compressor efliciency isob` tainedrgin spitefoff, the, s-hockl.s It is this control `of theshockf5waves'. thatmakes it. possible to obtain suchA higher:pressure-risesv in a single stage.

Features-.I of.v the invention ,relate to: the bla-ding ofthe-;o'mpre'ssorand..` the preferred embodiment ot:the'invention'hasbladesofnovelv shape andina particular: relation with one. another' foref.` fecting decelerationV of. gas! iow` aga-insti the back'. pressurevwith. control.; ofA the, shock Vwaves producing the. velocityy change.

Other olof|ects-v featuresand advantages of. the inventionfwill appearor hepointed-out as the-.descri-lotion prcceedsr In; the. drawing;formi-ng. a part-,thereof .in-.whichlike reference; characters indicatecorresponding I parts inA all. the views,

Fig, L is a` perspective View of. a compresso-r embodying thisVinvention, the casing being shown insectioni-norderv to:i-llustratei-the blading..

Fig. 2.is a fragmentary enlarged sectionalzview through-afpcrtion-oftherotor and stator of the compressor shown in Eig. 1I.. v

Fig. 3 is a development of the blading-a'lfeng thefcylinder A-Ao-f;1ig.,2. 1 rLheaxial.compressor shown inFig. 1 includes a casing `SI-l-iavfingan inlet opening. 9- at one end. Within,i thezcasing there is a fixed.stator hab IIL The gasor air enters the. compressor through the annularspace Il between the inside wall of.v the casing Il` andtheperipheralsurface ofthe stator hub.` The stator has. fixed blades I2 atequiangular positions around' its entire circumferenceand1t`heouter endsoi these blades are rigidly: 'co,nnectecl'` to theA casing 8..

2 Other stator blades t3' are similarlyv connected. to thecasing, andthe bladesl3 arespacedfrom' the blades IZto. leave room for a rotor I4having blades. II5- constructed. and arranged-Ito. draw air through.theA passages between the stator. blades I2, andto discharge. the. airthrough the. passages between. the stator blades I3'.

Fig. 2 shows the relation of one, oi the rotor. blades l5' to the stator4blades I2V and?. 3`. The outer edge ofA the. blade [5, extends., close`to the wall of the compressor casing 8;..andinthe con hstructionillustrated. the radial'` length oiV the blade, I5 isv slightly greatertoward'. its intake side. The internal. diameter. of the casing. 8devcreases proportionateli;f to leave, ample running clearance for theblade. it'.` `Constrnotion' avoids too rapid' an increase in the, crosssection of.' the passage betweensuccessive blades. I5.. Too rapid anincrease in the passage area. wouldjresult in dead air. regions in the,passages which would' lead `to reduced efficiency.

The. gas passages?" of` the. rotorare. the passages bounded on the sidesby successive rotorl blades, on the bottom by the surface I'I' of" therotor between blades, and on the` top by the i. side surface area of thecasing across which the outer ends ofl they bladesswe'ep as-tlie rotorr`e volves. The rotor can be constructed"with` a cylindrical shellconnectedwiththe. tips of the rotor blades. Such shrouds are used onturbines andA axi'alfflow compressors for the purpose, of preventing;tip clearance losses and.. for reducing` vibratiomand' are Wellunderstood in the art.

The rotor I`4` is connected with adrivngi shaft I8' that tunis inbearings within the compressor..

and power is appliedt'o thedrive'shat I`8'fron`1'a motor or anyexternal: source-of power;`

The priricilole` of the invention, the shape; ofv

the blades, and the correlation ofthe blades `can best beV unclersto'odvby considering. the` operation in connection with two successive.blades: wand As the. rotational speen"v of' anesnall flow' conf;-

pressor increased, a yspeed' is4 reached at'which the relative gasvelocity' vexceeds theloeal speed of' sound attsome; point on theblad'ing. Ifftnei ahead of the. leading edge off the adjacent blade I5.A shockwave of' this. type Whichkexists up.- streaml fromy the leadingedge ofi a. blade will be' referred to, herein. as a detachedll bowWaver These detached bow Waves existing. ahead' oi' each of the bladeseventually extend far out from the cascade and form an extended wavesystem. The losses due to this extended wave system are so large thatdesigners have avoided the occurrence of supersonic velocities in orderto avoid these losses.

In order to maintain the compressor eiciency it is necessary to have thebow wave move back far enough to attach tothe next successive blade l.Such attachment prevents the setting up of an extended wave system.

The amount that the bow wave moves back along the blade l5 depends u'ponseveral different factors. One is the blade speed. The bow wave tends tomove back as the velocity of the blade through the air increases.Another factor is the wedge angle, that is, the sharpness of the leadingedge of the succeeding blade I5. The bow wave moves back further, at agiven speed, ifV the leading edge of the succeeding blade is sharp. Ifthe angle of the blade surfaces that meet to form the leading edge isgreater than 90, it is not, possible in air to get attachment no matterhow high the blade speed may become. Another factor affecting theultimate position of the bow wave is the width of the narrowest sectionbetween the blades, that is, the area of cross section of the spacebetween the blades I5 and I5 in a plane normal to the direction of thegas flow between the blades. If there is any considerable reduction insection along the passage between the blades the bow waves cannot becomeattached to the blades. For reasons that will become apparent, it isdesirable to have a slightly restricted throat between the blades, andto have the shock wave between the blades downstream of the minimumsection of the passage between the blades.

The position of the bow wave is affected also by the back pressureratio, that is, the ratio of back pressure to inlet pressure. A higherback pressure ratio opposes downstream movement of the bow wave, butwith sonic or supersonic velocity of the air at the minimum throatsection 34, the back pressure ratio is not directly effective ontheposition of the detached bow wave.

If,`however,the throat section is large enough, 'the back pressure lowenough, the wedge angle small enough and the rotational speed highenough the bow waves become attached. The portion of the waves upstreamfrom the cascade then nearly disappears and the portion between theblades moves downstream and is confined entirely within the blading.rIhis confined shock decelerates the air thru the speed of sound and inthis process compresses the air efciently.

Although it is possible to accelerate gas to supersonic velocity withoutshock, it is not possible to decelerate through the sonic velocitywithout having a shock wave in the gas stream.

V`In the operation of the compressor, the rotor is driven atsufficiently high speed to make the relative velocity of the airentering the rotor blading higher than the sonic velocity. The airvelocities relative to the stator blades, both inlet and discharge, issubsonic and the design of the stator blading is conventional.

` The blade surfaces at the leading edge meet in an angle less than 30degrees and preferably less than 20 degrees. In the illustratedembodiment of the invention the blade faces form an angle ofapproximately degrees at the leading edge. The leading edge thus forms asharp wedge so that bow waves can become attached to 4 the blades. Inthis specification and in the claims, the term sharp as applied to theleading edge designates an edge in which the effective angle between theforward and rearward blade surfaces is less than 30 degrees, and theleading edge radius is less than 2 percent of the circumferentialdistance between the leading edges of successive blades; or the bladesare made of such thin material that the thickness of the leading edge isless than 2 percent of the circumferential distance between blades.

The cross-sectional area of the inlet of the gas lpassage between theblades I5 and I5 is indicated by the plane 33. All gas passagecrosssections referred to in this specification and in the claims areareas of planes normal to the direction of gas ow through the passage atthe location where the cross-section is taken.

As the result of the increase in thickness of the blades l5 and I5downstream from the passage inlet 33, the cross-section of the rotor gaspassage between these blades decreases progressively to a throat section34 where the crosssectional area is a minimum, but not substantiallyless than the passage entrance or inlet 33. The area of the throatsection 34 is approximately 93 percent of the cross-section of the inlet33 in the compressor shown in the drawing. This value is given merely asan illustration.

The back pressure at the discharge-region 35 is so correlated with theinlet pressure and the rotor speed that the air flow decreases throughthe sonic velocity and undergoes normal shock at the region 36 justdownstream from the throat 34. The gas passage between the blades l5 andI5 increases in cross-section beyond the throat 34, and this insuresstability of the shock wave.

Although the shock wave tends to be substantially normal to thedirection of gas flow, it is, in practice distorted by interaction withthe boundary layers on the blades, the rotor and the casing. Angularwaves given off from the boundary layers interact with the normal shockand sometimes result in multiple reflections. In the compressor of thisinvention, this entire normal shock complex is conned within the bladepassage in the region 36; and the term region of shock, as used herein,refers to the space occupied by this normal shock complex.

the walls of the rotor gas passage. The blading,

therefore, must have sufficient chord length from the leading edges 3|to the trailing edges 31, as compared with the spacing between theblades, so that planes normal to the gas flow throughout the region ofshock is bounded on both ends by the blade surfaces; and it is importantthat this be true at the top as well as at the lower ends of the bladeswhere they connect to the body of the rotor, and are closer togetherthan at their tips.

I In order to reduce the intensity, and hence the energy losses, in thenormal shock complex at the region just beyond the throat 34, therearward surface of each of the blades I5 is made with a concave portion39 for a short distance back from the edge 3|. This concave regionIoriginates compression waves which reduce the velocity of the airsmoothly before the air reaches the region of normal shock. Thesecompression waves will thus reduce the intensty of the shock and thelosses that go with it;

In order that supersonic*flbvvi intc the-fcascade mayl be startedyi-tisneces'sary that the narrowestsectioriof the passaaes-formed by theblades downstreamfrom the inlet section 33 be nearly as large as theareaavailable for gas ow at the inlet section 33. In starting the machine,an extended-'wave system is set up in the air and this entails largelosses. In order tot haveV the desired fiowconditions; setup, itisnecessary that the air after undergoing these large losses, be stilltcapable. of passing through the blading. If atlrroat with considerablylessair flow area than theinlet` section 3'3 were included in the -bladedesigmthen it wouldnot be. possible for the air to get;throughthisthroat in` the starting condition, and the vdesired"flowconditions'- could not be set up.

It will be understood that the blades l5 of the rotor may be used in thestator on the *discharge side of a rotor that delivers the gas to thedownstream stator blades at supersonic velocity. The relative velocityofthe blades and gas is the important consideration whether or not theblades are moving in space. The term cascade is used herein to designatea circle of blades whether secured to a rotating or stationary part ofthe apparatus. In any event, the blading offers the advantage that thegas having supersonic velocity with respect to the gas passages candecelerate to a subsonio value with the shock waves contained entirelywithin the blade passages.

In the case of stationary blading the forward and rearward surfaces ofthe blades are the surfaces corresponding to the forward and rearwardsurfaces of the blades when used on a roy tor. The direction of the `airentering the passages between the blades has both an axial and latangential component, and the direction of the tangential component istoward the f-orward surfaces of the blades and away from their rearwardsurface.

The preferred embodiment and method of this invention has beenillustrated and described, but `changes and modifications can be madeand some featuresof the invention can be used in diierent combinationswithout departing from the invention as defined in the claims.

I claim as my invention:

1. A supersonic compressor including a cascade of blades, angul-arlyspa-ced from one another around a surface of revolution, said bladeshaving sharp leading edges which'are disposed at acute angles to a planenormal to the axis of the body of revolution and being of suicient chordlength so that successive blades intersect common parallel planes thatare spaced from one 'another by a substantial distance and that arenormal'to the direction of gas now between the blades, the confrontingfaces of said blades diverging from one another in the direction of gasnow for at least a portion of their length between the parallel planes.

2. A supersonic axial-flow compressor comprising a casing, a bladedrotor supported within the casing for rotation with running clearancebetween the blade tips and the inside surface of the casing, angularlyspaced blades on the rotor with sharp leading edges disposed at acuteangles to both the axis of rotation and the plane of rotation of therotor, said blades being of suiiicient chord length so that successiveblades intersect common parallel planes that are spaced `from oneanother by a substantial distance 4and that are normal to the directionof gas 'new' between the: biaces=,{ the l weborama faces of said bladesdiverging from one another in the direction of gas flow' for atleastapos#- tion of their length betweengthe parallel planes.

3. A supersonic axial-how` compressor` coni- DI'SIL,4 a Cascade haV'ngangulgfly; Spacedprofor rearward face just beyond the leading edge ofthe blade, each of said blades increasing in thickness along the portionof its length that has said concave surface.

5. An axial-flow compressor for gas having supersonic velocity, saidcompress-or comprising a casing and a bladed rotor that rotates withinthe casing with running clearance between *thel blade tips of the rotorand the inside surface of the casing, said rotor having blades ofsulcient chord length to enclose a gas passage in which a planeperpendicular to the gas ilow through the passage intersects theconfronting faces of the blades that form the gas passage along a regionof the passage where the blades areshaped to provide rst a throat andthen a region of expanding cross-section in the direction of gas flow,the blades having concave surfaces on their rearward faces at regionsspaced va short distance beyond the leading edges of the blades forcontrolling the gas velocity, each of said blades increasing inthickness along the portion of its length that has said concave surface.

6. A supersonic axial-flow compressor comprising a stator, a rotor, andblades on the rotor having leading edges formed by forward and rearwardblade faces that meet in an effective angle of less than 30 degrees, andwith the bisector of such angle at an acute angle to the plane ofrotation of the rotor, the rearward faces of the blades just behind theleading edges being concave for controlling the velocity of iow, each ofsaid blades increasing in thickness along the portion of its length thathas said concave surface and successive blades of the rotor being ofsufiicient chord length to intersect common parallel planes that arespaced from one another by a substantial distance and that are normal tothe direction of gas ow between said blades, the confronting faces ofsaid blades diverging from one another in the direction of gas flow forat least a portion of their length between the parallel planes.

7. An axial-now compressor including a stator, a rotor having blades formoving gas from the stator at supersonic veloci-ties with respect to theleading edges of the rotor blades, successive blades being shaped toprovide gas passages with entrances that have a cross section slightlylarger than the cross-section of the passages at an intermediate thro-atregion, and said blades `being of suicient length so that successiveblades intersect common parallel planes that are spaced from one anotherby a substantial distance and that are normal to the direction of gasflow in the passage just beyond the throat in the downstreamY direction,the confronting faces of said blades diverging from one another in thedirection ci gas flow for at least a portion of their length that liesbeyond the throat but between the parallel planes.

- 8. A supersonic velocity compressor including a cascade of bladesangularly spaced around a surface of revolution and havingr leadingedges at their upstream ends and portions of greater thicknessintermediate their ends providing surfaces that cooperate Wit-hconfronting surfaces of preceding and succeeding blades to form gaspassages that decrease slightly in cross section to a throat area, somedistance back from the leading edges of the blades, and then increase incross section toward the outlet ends of said passages, and concavesurfaces on the rearward faces of the blades upstream from said throatareas.

ARTHUR KANTROWITZ.

REFERENCES CITED The following references are of record in the nie ofthis patent:

UNITED STATES PATENTS Number Name Date 408,864 Vogelgesang Aug. 13, 1889853,363 Holzwarth May 14, 1907 997,678 Jalonick July 11, 1911 152,378,372 Whittle June 12, 1945 2,435,236 Redding Feb. 3, 1948

